Most modern wind turbines are controlled and regulated continuously with the purpose of ensuring maximum power extraction from the wind under the current wind and weather, while at the same time ensuring that the loads on the different components of the wind turbine are at any time kept within acceptable limits. Desirably, the wind turbine may also be controlled to account for fast local variations in the wind velocity—the so-called wind gusts, and take into account the dynamic changes in the loads on the individual blades due to e.g. the blade passing of the tower or the actual wind velocity varying with the distance to the ground (the wind profile).
To this purpose most modern wind turbines comprise a number of sensors placed on different wind turbine components such as e.g. on the blades, the nacelle, the hub, the foundation, or on the tower. The parameters measured by these sensors are collected and monitored by the wind turbine controllers and following some control strategy the optimal control parameters of the turbine in order to perform optimally under the given conditions are determined. The methods of controlling the current performance, and thereby the power production and the load situation of the wind turbine, include for instance pitching of the blades, adjusting any other active aerodynamic devices for changing the aerodynamic surfaces of the blades such as flaps or vortex generating means, adjusting the power, and/or adjusting the rotational speed of the rotor. The parameters measured by the different wind turbine sensors may for instance include the current wind speed and direction, the wind shear and turbulence, the rotational speed of the rotor or the generator, the pitch angle of each blade, the yaw angle, accelerations, stresses or vibrations, and may be measured by sensors such as accelerometer, anemometers, strain gauges, optical fibres etc.
As the sensor measurements play an important role in the control of the wind turbines and thereby directly or indirectly influence the loading on the different wind turbine parts or e.g. the energy production, the accuracy and general performance of the sensors is correspondingly important. However, most often there is no regular calibration or maintenance of the sensors. Further, manual calibration and inspection may require a service team on site which is both very expensive, time consuming, and difficult to administrate.